Dr. Dan Talks Agronomy

Seed Between the Rows

Seeding cover crops into standing corn helped New York growers get a jump on the fall season last year. Timely planting is critical in northern climates in particular. (Photo courtesy of Jonathon Martin)

Getting cover crops planted in a timely manner is a challenge for farmers in a corn/soybean rotation.

One way to get a jump on fall is to interseed cover crops into standing corn after the V4 leaf stage. Corn is about 30 inches tall at this stage and should be competitive enough to compete for nutrients without a yield sacrifice.

Jonathon Martin, an agronomist with Auburn Ag Products, based in Auburn, New York, worked with several growers on this approach in 2015. He used a 12-row toolbar equipped with a Valmar air seeder and Dawn Biologic inter-row units with twin disc openers spaced 7.5 inches apart and used airbags for down pressure.

The cover crop was interseeded into 750 acres of standing corn across a number of fields during the last week of June and into the first week of July. Corn hybrid maturities ranged from 96- to 108-day and included silage and grain hybrids that had been planted the first half of May in 30-inch rows. No additional nutrients, such as nitrogen, were applied in this test.

The cover crop cocktail, recommended by Cover Crop Solutions, included 2 pounds of radishes, 3 pounds of crimson clover and 10 pounds of annual ryegrass. Seed cost was $22 to $23 per acre and seeding cost was $21 per acre.

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The cover crops were interseeded between V4 and V7 leaf stages. "We know that once corn gets to V6, any seeds that germinate don't reduce corn yield. We also learned that once the corn gets to V8, it is too tall to seed and stalks on some varieties will snap off at V7," Martin said.

He added that the covers established quickly before the corn rows canopied over. Once the corn shaded over the inter-rows, cover growth stopped and the plants took on a yellowish appearance.

"Some of the acres interseeded were silage corn, and with the high population density, height and excess growth, the covers looked very poor by August. However, once the silage was cut off, they recovered and bounced back nicely," Martin said. "Trafficking with semis during harvest had no long-term impact on growth. And for the corn harvested for grain, once leaves begin to die and fall off, sunlight penetrated the canopy and the covers grew quickly," he said.

Will interseeding into standing corn pull too much moisture from the soil and rob the corn crop? Generally, when cover crops such as covers with taproots are shaded, they are very slow growing and almost go dormant during the summer. The key is to select species that survive shade but aren't so competitive with corn that they become like a weed. You certainly don't want the equivalent of foxtail, for example.

The New York's Finger Lakes region typically has enough moisture to support the practice of interseeding. "We naturally have the water, and air temperatures aren't too hot during the summer," he said. "The growers felt there was no negatives and maybe there was even a positive benefit to the corn. However, they need to get used to the covers' stunted look during the summer."

Ryegrass survived best, followed by radishes in the New York trials. Radishes are a cool-season species and planting them into warm soil during the warm summer did reduce their growth potential in this test. Martin noticed crimson clover didn't handle the competition with ryegrass as well as hoped. Next year, he plans to replace crimson clover with hairy vetch.

Trials were also conducted to compare the fall growth of drilled and interseeded cover crops. In mid-September, after silage harvest, annual ryegrass was drilled alongside the interseeded cover crop cocktail in a separate block. Two months later the drilled ryegrass measured 6 inches tall compared to the 18-inch-tall covers that had been interseeded. Martin said they saw similar growth patterns when covers were interseeded in to corn harvested as grain.

There are many innovative ways of interseeding being developed. I'd like to hear about your experiences so we can learn together about this practice.

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Dan Davidson

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